1. Field of the Invention
The present invention relates to automatic assembly systems and particularly to a system for the selection and delivery of preoriented rivets or like fasteners to one or more riveting machines.
2. Description of the Related Art
The procedure of assembling parts by means of riveting is used in numerous industries, in particular in the aerospace industry. During the evolution of this technology, a large number of automatic riveting machines have been developed, which according to the parts to be assembled, are able to install different kinds of rivets or like fasteners and for each kind, to finalize the choice of different lengths depending upon the thickness of the sheets to be joined.
Rivets or like fasteners are usually supplied from a suitable rivet feeding system capable of selecting and sending, time after time, the right kind and length of a requested rivet to the riveting machine.
With the development of continuous numeric control (CNC), modern automatic riveting machines are capable of assembling a large number of different parts and of storing the program which assigns the position of each rivet to be installed. The machines are also able to accurately finalize the correct call of the right kind and length of the rivet to be installed.
Typically, the type of rivet to be used is assigned by the designer and stored in the memory of the control while the length is chosen upon measuring, time after time, the thickness of the parts to be connected together.
Rivets are consequently requested with an unpredictable sequence and they must be delivered in a very short time in order to prevent the cycle time from being increased.
Several automatic rivet feed systems are known, in which all rivets of the same kind and same length (identical) are stored inside a vibratory bowl which orients and accumulates the rivets on a track, usually horizontal, whereby rivets are withdrawn one at a time and are pneumatically transferred via a tube to the riveting machine.
In addition to such systems, other automating riveting machines are known, such as spirals or cassettes, in which the different rivets are disposed and preoriented inside a "cartridge". Such magazines feature a certain capacity and usually are mounted close to the riveting machine.
Both these approaches to the problem of automatically feeding a riveting machine by delivering to it, one-by-one, a preoriented rivet selected from a certain inventory of rivets, suffer several drawbacks and/or limitations.
In the systems using a vibrating bowl, each bowl is dedicated to a precise kind and length of the rivet and such systems are consequently very expensive and bulky. In fact, it is sufficient to think of a system capable of handling five different kinds of rivets and for each of them at least ten different grip lengths to have an idea of the costs and size involved. Furthermore, a feed station featuring fifty or more bowls cannot be mounted on a board of the machine due to weight and size limitations, and consequently, the station needs to lie on the floor and to be connected via tubes to the riveting machine with a related performance drop in terms of delivery time.
The "cartridge machines" are, on the one hand, more compact but, on the other hand, they need continuous replacement and involve high costs related to their preparation.